As a known container sealing device used for a container with an inner plug, there is a structure which is provided with the inner plug and an upper lid; and in which a cylindrical part fitted with an opening part of a container and a separation part continuously provided on an inner side thereof via a score are provided in the inner plug (refer to FIGS. 1 and 2 in Patent Literature 1).
In this container sealing device, the upper lid is preliminarily engaged (screwed) with the separation part of the inner plug through, for example, reverse threads, and the separation part of the inner plug is screwed to a connection part of the upper lid by screwing backward the upper lid so as to remove it from the mouth part (forward thread) of the container when the plug is to be opened, whereby the separation part is separated from the cylindrical part of the inner plug and the separation part is held by the upper lid. According to this cap structure, the plug can be easily opened only by loosening the upper lid, and the separated separation part is held by the upper lid, and thus the separation part does not become so-called rubbish and also can be made to function as a seal.
Incidentally, the aforementioned technology is to unseal the plug by loosening it (by rotating the plug counterclockwise thereby fracturing the score provided in the plug) and to remove the upper lid from the mouth part of the container after unsealing the plug. Recently, a type of technology in which the plug is unsealed by tightening the upper lid (rotating the upper lid clockwise thereby fracturing the score provided in the plug) and the upper lid is removed from the container after unsealing the plug by rotating the upper lid counterclockwise has spread in the market, and there is a concern that a user is upset when opening the plug.